United States nuclear giant General Atomics has lifted a buyout bid for the 25 per cent of the Four Mile uranium mine that it doesn't already own, causing shares in ASX-listed Alliance Resources to rocket by almost 50 per cent.

General Atomics, through its subsidiary Quasar Resources, already owns 75 per cent of the Four Mile mine in far north South Australia and has made a new cash offer to buy Alliance's stake of 25 per cent plus the target's share of uranium oxide concentrates already mined, for a total price of $71.3 million.